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Unanswered Questions

Warm Cows Are Happy Cows April 2017

My daughter is in 4H and has a calf we are raising in a shed behind the house. Recently, the bulb burned out on the heat lamp we leave on to keep the cow warm. Is there a simple circuit I could use to remotely monitor the temperature and alert me if it drops below a set point? I know there are remote temperature gauges but I need one with an alert or a way to hack one to add an alert. Any ideas welcome.

Robert Lowery
Florence, SD

POTS Ring Generator April 2017

I need a circuit to generate 20 Hz 90 VAC to ring a POTS telephone on a theater stage. That’s Plain Old Telephone System vs. Pretty Advanced New Stuff (PANS) for the younger readers. If I could locate an old crank ring generator, it would work but would not be as convenient.

Dale Carlsen
Woodbridge, VA

Ni-Metal Hydride Battery Chargers April 2017

Now that Ni-Cad batteries are becoming an endangered species, is there any way to convert their chargers to work on the newer and ecologically sounder Ni-Metal Hydride batteries? I read that the Ni-Metal batteries have very different charging requirements rather than the constant current chargers for Ni-Cads. I have several bench chargers, not to mention a multitude of “wall warts” that I would like to modify.

Michael Herman
La Quinta, CA

Surround Sound Questions March 2017

I recently upgraded from an older two-channel stereo system to a 5.1 surround sound receiver. I have left, right, center, and sub woofer speakers set up at the front of the room, but no easy way to run wire for the rear speakers.

What’s the best DIY wireless method to get my surround sound to the back of the room?

Does someone have a schematic for a stereo transmitter/receiver that I could build? Would using a combination wired and wireless setup  have any issues with syncing the front and rear channels?

Dustin Quintanilla
San Luis Obispo, CA

Laser Flashing March 2017

I need help with a circuit design to flash a 10W laser diode at 14 Hz. A crystal controlled 555 IC is too variable due to temperature, and must be calibrated. No microcontrollers please; too complex and require coding. I need a simple discrete design.

The problem is laser diodes are pulsed with a tiny duty cycle, so they must be pulsed at high PRF to create the 1/28 second ON cycle. Probably 100 kHz for 1/28 second, off for 1/28 second, repeat ... It may require multiple laser diodes, interleaved ON pulses to smooth out the 14 Hz ON cycle. I basically want to emulate as close as possible the 14 Hz square wave. To top it off, this needs to run off the “dirty” rectified 6-12 VDC from a motorcycle alternator.

As an alternative, instead of laser diodes, an array of LEDs, perhaps 6 x 6 (36 LEDs) may be acceptable to simplify down to just a 14 Hz crystal controlled strobe timer.

The whole thing needs to fit in a garage door opener sized box.

Tom Uryga
Hillsboro, OR

Reliable Voltage Source March 2017

I am designing a battery powered circuit that requires a very reliable voltage source. I was considering using a zener diode in series with a resistor across the power source and then tapping it at the diode/resistor for the power point, but it seems this would be very wasteful for the battery. Would I be better off with a linear regulator like an LM317 and if so, would it create as accurate a voltage?

Gilbert Kreps
Midland, TX

Getting Started With High Voltage March 2017

I would like to experiment with high voltage projects, but all my experience in building power supplies is for low voltage (typically 5 or 12 volts). I’d love a schematic for a high voltage power supply that could produce between 0 and 250 volts safely. Also, any safety pointers for getting started would be appreciated.

Ed Warren
Everett, WA

Vehicle Detector February 2017

Does anyone have suggestions for buying or building a vehicle detector which can be used with the Arduino? I wish to sense and count passing vehicles.

Robert Johnson
Bolton, MA

LED Compatibility? February 2017

I replaced some outside 60W bulbs with CREE dimmable LED replacements. The lamps are  controlled and dimmed using X10 switches. When switched off, the lamps still glow at about 20% and will not shut off completely unless I use the disable feature of the switch. However, this prevents the timer from automatically controlling the lights. What causes this and is there a fix, or are LED replacements not compatible with X10?

Christoffer Mortensen
Piscataway, NJ


Conventional x10 switches require a small current to run through the load (i.e. an incandescent light) in order to work correctly. For non incandescent loads such as CFL or LED lights you need a x10 switch specifically made for them. I currently use a WS13A x10 wall switch and also an XPFM x10 fixture module to switch LED lights (and CFLs). These x10 switches are not dimmable though. In general, LED lights need a dimmer specifically made for LED lights. I have had a good success with Lutron CL digital dimmer (e.g. MACL-153MH) as a manual dimmer but I do not know of an x10 compatible dimmer designed for LED lights. Perhaps someone else knows of one that will work.

Dan Koellen
Roseville, CA

I go through this problem whenever I use x10 in a small project. x10 appliance modules need some kind of load resistor, but due to the 110VAC appearing when it turns on, I do not advise it. Instead, a batter way to solve it is to connect a 110VAC relay parallel to the LED bulb. If you want to use a resistor 33K 1W will be OK (I tested up to 42K that works), BUT be very careful about insulating the wire leads. I tested both methods (resistor turn on only a second in on state), they work perfectly.

Ankur M Bhakta
Tulsa, OK

Three-Way LED Flasher February 2017

I need a simple circuit to sequentially flash three separate strings of 10 LED lights. Flashing two strings is easy; three is tougher.

Michael Herman
La Quinta, CA

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